On the coupling of lunisolar resonances for Earth satellite orbits

The resonance C1 occurs when the longitude of the perigee measured from the equinox becomes a slow angle in the doubly averaged equations of motion. This resonance is one of the critical inclination family with I 46°. For prograde Earth satellite orbits, up to five critical points can be identified. Only simple pitchfork bifurcations occur for the single resonance C1. A two degrees of freedom system is studied to check how a coupling of two lunisolar resonances affects the results furnished by the analysis of an isolated resonance case. In the system with two critical angles (g+h and h,+2 , seven types of critical points have been identified. The critical points arise and change their stability through 11 bifurcations. If the initial conditions are selected close to the critical points, the system becomes chaotic as shown in Poincaré maps.     

On the screening of the interstellar electric and magnetic fields by the solar wind

Fast-streaming solar-wind plasma with high conductivity screens the heliosphere from the penetration of the interstellar electric and magnetic fields. The simplest model with the constant solar wind conductivity and radial velocity is considered and the boundary electrodynamic problem is solved for static external fields. The results show that screening of the external fields takes place in the heliosphere according to the exponential law.     

Heating of the interstellar medium by the solar wind

The heating of inflowing interstellar gas by the solar wind is calculated. The experimental differential cross sections have been used for calculating electron-H(He) and proton-H(He) elastic scattering rate coefficients. The solar wind is assumed to be a two-component (protons and electrons), steady, spherically symmetric stream moving radially outward, with the inflowing gas following Keplerian trajectories. The spatial distributions of effective temperature increase within interplanetary space have been obtained.     

Ionization of interstellar matter by suprathermal dust grains

Suprathermal dust grains as suggested by Wickramasinghe produce electrons of energies not higher than 20 eV by Coulomb collisions with free electrons in an interstellar medium. These electrons are responsible for the production of singly ionized ions but not effective for that of highly ionized ones. This explains a general feature of the composition of atoms and ions as observed from the Copernicus satellite.     

On the band-to-continuum intensity ratio in the infrared spectra of interstellar carbonaceous dust

Published interpretations of the relative intensity variations of the unidentified infrared bands (UIBs) and their underlying continuum are discussed. An alternative model is proposed, in which a single carrier for both emits (a) mostly a continuum when it is electronically excited by photons (visible or UV), or (b) exclusively the UIBs, when only chemical energy is deposited by H capture on its surface, inducing only nuclear vibrations. The bands will dominate in atomic H regions but will be overcome by thermal continuum radiation when the ambient field is strong but lacks dissociating photons (900–1100 Å). The model applies to photodissociation regions as well as to limbs of molecular clouds in the interstellar medium and agrees quantitatively with recent satellite observations. It gives indications on atomic H density and UIB intensity provided the ambient radiation field is known. It invokes no chemical, electronic, structural or size change to interpret the observed intensity variations.     

Filaments within the Perseid meteoroid stream and their coincidence with the location of mean-motion resonances

Positions of 17 filaments found inside the Perseid meteoroid stream by method of indices are compared with those of low-order mean-motion resonances with Jupiter and Saturn. By this comparing, the Jupiter and Saturn branches of the Perseid stream were identified. The existence of gaps in the distribution of the semi-major axes of the Perseids is confirmed using the more numerous material of a new version of the IAU Meteor Data Center Catalogue. Our integrations of the motion of particles in the Perseid stream lead to an extraordinary important fact. The found filaments are located in close proximity of strong resonances. They represent, with a high probability, increased numbers of particles gravitationally expelled from a resonant gap and (temporary) settled down in its close proximity.     

On the timing of an interstellar communication

By considering prominent events that are observable from both Earth and nearby stellar systems it is possible to establish common clocks that may be useful in estimating arrival times for signals of intelligent extraterrestrial origin. The geometry and statistics of a timing strategy are developed together with quantitative estimates of its effectiveness and limits on its application. Effectiveness is measured by comparing the timing strategy with one randomized in time. Limitations arise from inaccuracies inherent in the determination of stellar parallaxes and result in standard deviations of the order of weeks to months for time estimates. The problem can be alleviated by choosing clocks close to Sender in angular distance. Signal opportunities for several nearby Sun-like stars are calculated using the bright Nova Cygni 1975 as a clock.     

Periodic orbits in the generalized perturbed restricted three-body problem

This paper studies the existence and stability of equilibrium points under the influence of small perturbations in the Coriolis and the centrifugal forces, together with the non-sphericity of the primaries. The problem is generalized in the sense that the bigger and smaller primaries are respectively triaxial and oblate spheroidal bodies. It is found that the locations of equilibrium points are affected by the non-sphericity of the bodies and the change in the centrifugal force. It is also seen that the triangular points are stable for 0<μ<μ _c and unstable for m_c ￡ m < \frac12\mu_{c}\le\mu <\frac{1}{2}, where μ _c is the critical mass parameter depending on the above perturbations, triaxiality and oblateness. It is further observed that collinear points remain unstable.     

On the stability of the solar wind

The stability of the solar wind is studied in the case of spherical symmetry and constant temperature. It is shown that the stability problem must be formulated as a mixed initial and boundary-value problem in which are prescribed the perturbation values of velocity and density at an initial time and additionally the velocity perturbation at the base of the corona for all times. The solution is constructed by linear superposition of normal solutions, which contain the time only in an exponential factor. The stability problem becomes a singular eigenvalue problem for the amplitudes of the velocity and pressure perturbations, since additionally to the boundary condition at the base of the corona one must add the condition that the amplitudes behave regularly at the critical point. It is proved that only stable eigenvalues exist.     

Desorption of molecules from interstellar grains and the heating of dust clouds

Temperature fluctuations induced in very small (r10^–3 ) interstellar grains by the absorption of photons from the ultra-violet radiation field or by energy released on molecule formation are shown to lead to significant gas heating due to thermal desorption of condensed atoms or molecules. For clouds with N(H)=1–10×10²⁰ cm^–2, heating rates due to this process are comparable to direct heating by cosmic rays or grain photoelectrons.     

Disintegration of dust aggregates in interstellar shocks and the lifetime of dust grains in the ISM

We have studied to influence of grain porosity on the dust destruction mechanism in interstellar shocks. Our results show, that fluffy aggregates of dust grains can be broken up easily in shocks.     

On periodic orbits of the second generation and regions of stability

A part of the familyh of retrograde periodic orbits of the restricted problem (μ=0.5) is examined in relation to the families of periodic orbits of the second generation branching from it. Many such families are determined and the significance of the configuration of their characteristics for the determination of the boundary of the stability region around this part ofh is discussed.     

On stability of orbit of artificial moon moving around a small celestial body perturbed by an external body

We examine the stability of the orbit of an artificial moon of a small celestial body in the presence of an external massive perturbing body in terms of the restricted three-body problem. The orbit of this moon is shown to be dependent on the shape of the small body and central gravitational field of the external body. We study how these factors interact with each other and how they affect the stability of the orbit.     

Distribution of hot stars and interstellar dust in Carina

Translated fromAstrofizika, Vol. 36, No. 2 pp. 165–180, April–June, 1993.     

Shattering and coagulation of dust grains in interstellar turbulence

We investigate shattering and coagulation of dust grains in turbulent interstellar medium (ISM). The typical velocity of dust grain as a function of grain size has been calculated for various ISM phases based on a theory of grain dynamics in compressible magnetohydrodynamic turbulence. In this paper, we develop a scheme of grain shattering and coagulation and apply it to turbulent ISM by using the grain velocities predicted by the above turbulence theory. Since large grains tend to acquire large velocity dispersions as shown by earlier studies, large grains tend to be shattered. Large shattering effects are indeed seen in warm ionized medium within a few Myr for grains with radius   a ≳ 10⁻⁶  cm. We also show that shattering in warm neutral medium can limit the largest grain size in ISM  ( a ∼ 2 × 10⁻⁵ cm)  . On the other hand, coagulation tends to modify small grains since it only occurs when the grain velocity is small enough. Coagulation significantly modifies the grain size distribution in dense clouds (DC), where a large fraction of the grains with   a < 10⁻⁶ cm  coagulate in 10 Myr. In fact, the correlation among   R_V   , the carbon bump strength and the ultraviolet slope in the observed Milky Way extinction curves can be explained by the coagulation in DC. It is possible that the grain size distribution in the Milky Way is determined by a combination of all the above effects of shattering and coagulation. Considering that shattering and coagulation in turbulence are effective if dust-to-gas ratio is typically more than ∼1/10 of the Galactic value, the regulation mechanism of grain size distribution should be different between metal-poor and metal-rich environments.